Speakers for acoustic devices comprise a membrane which is actuated by a so-called voice coil. For an improved translative movement of the membrane often a so-called corrugation is formed at the membrane around the area in which the voice coil is fixed to the membrane. This corrugation forms a joint, articulation or pivot so that the portion of the membrane which is closer to the center of the membrane than the voice coil, i.e. the portion which forms the interior portion of the membrane is moved more or less translational. However, in case the acoustic pressure exceeds a limit pressure the thin membrane is bulged which leads to a decreased performance of the speaker. Thus, in some cases a plate is fixed to the membrane in the central portion of the membrane in order to stiffening the central portion. However, although such a plate may reduce the bulging, still one or even several oscillations are superimposed to the movement of the membrane. Furthermore, in case a given frequency is exceeded the plate, due to its mass, cannot follow the movement induced by the voice coil and holds still. This given frequency is called cut-off frequency.